The compressive load carrying capacity of a body or layer of elastomeric material may be increased several hundred percent by incorporating a plurality of spaced, parallel laminae fabricated of nonextensible material and oriented generally perpendicular to the direction of the compressive load. The laminae increase the compressive load carrying capacity of the elastomeric material by restricting the ability of the material to deflect or bulge in directions transverse to the direction of the compressive load. Specifically, the laminae effectively subdivide the force-free or non-loaded surfaces that extend between the loaded surfaces of the elastomeric material. When loaded in compression, therefore, the material cannot deflect along its force-free surfaces in a large bulge that is continuous between the loaded surfaces of the material. Instead, the "subdivided" force-free surfaces can only deflect in a series of distinct and separate smaller bulges.
The total volume of material in the smaller bulges of a laminated elastomeric structure is significantly less than in the large single bulge that appears in an unlaminated body of elastomeric material. Thus, for a given load, the laminated structure exhibits a smaller change or reduction in height or length than would be experienced by the same body of elastomer without laminae. Since the height or length reduction is a critical parameter for practical use of elastomeric material under compressive loads, the compressive load carrying capacity of the material is increased. At the same time, the ability of the material to yield in shear or torsion in directions parallel to the laminations or transverse to the direction of the compressive load is substantially unaffected.
The characteristics of laminated elastomeric bearings have resulted in the commercial acceptance of the bearings for a variety of applications. Nonetheless, the basic design concept on which the bearings rely also has an adverse effect on their acceptability. In particular, to increase the compressive load carrying capacity of a laminated bearing, while maintaining a specified torsional or translational shear deflection capability, the number of non-extensible laminations must be increased. The non-extensible material is often a high-strength and expensive metal, such as titanium or stainless steel. For many bearing configurations, the metal must be carefully machined, at extra cost. In addition to the expense of the nonextensible laminations, they represent a significant portion, if not substantially all, of the weight of a laminated bearing. The increased cost and weight of higher capacity laminated bearings have thus placed limitations on their commercial acceptance.
Another approach to increasing the compressive load carrying capacity of a layer of elastomeric material is to restrict the ability of the material to bulge by enclosing the force-free surfaces of the material in a circumferential shell or housing. Rosenzweig U.S. Pat. No. 2,359,942 and Wallerstein, Jr. U.S. Pat. No. 3,081,993 both describe and illustrate resilient mountings in which the force-free surfaces of a body of elastomer are partially or wholly enclosed by a bulge-restricting shell. In the Rosenzweig mounting, the body of elastomer is completely encased in a rigid metal housing. Nonetheless, the elastomer is free to bulge to a limited extent because of an annular body of resilient material interposed between the body of elastomer and the rigid housing. The intermediate resilient material is significantly more compressible than the elastomer (i.e., it has a lower Poisson's ratio), and can be compressed by, and to accommodate, bulging of the elastomer. In the Wallerstein, Jr. mounting, a relatively wide, split metal band encircles a cylindrical body of elastomer. A garter spring normally prevents the ends of the band from separating. Thus, when the mounting is loaded in compression, the band initially prevents the central longitudinal portion of the body from bulging. When a predetermined compressive load is reached, however, the elastomer forces the split band open against the resistance of the garter spring. The mounting thereafter deflects or bulges at an increased rate for higher compressive loads.
Although both the Rosenzweig mounting and the Wallerstein, Jr. mounting may be effective in increasing the compression load carrying capacity of a body of elastomeric material, neither mounting is intended to accommodate significant torsional or translational shear motions. In the Wallerstein, Jr. mounting, for example, translational shearing movements between the rigid end members 2 and 3 that are secured to the body of elastomer can only be accommodated by shearing of the unconfined end portions of the elastomer. Similarly, the frictional engagement between the split band and the exterior surface of the elastomeric body effectively prevents the confined central portion of the elastomeric body from deflecting in torsional shear. The Rosenzweig mounting is constructed such that translational movements between a supported and a supporting member stress the elastomer of the mounting in compression, rather than shear. Relative rotation between the supported and supporting members will be strongly resisted by the friction developed between the body of elastomer and the adjacent, radially extending metal parts. A particular problem will be the friction developed beween the elastomer and the lower supporting washer 6 and the related friction developed between the washer 6 and the abutment ring 5.
The use of a bulge-restraining housing or shell in an elastomeric mounting that is intended to accommodate both compressive and torsional loads has been suggested by Irwin U.S. Pat. No. 3,504,905. In the mountings or bearings of the Irwin patent, particularly the bearings of FIGS. 7, 8 and 9, an openwork mesh of wire, for example, encloses the circumference of a laminated elastomeric bearing. The mesh impedes, but does not prevent, the lateral extrusion or bulging of the elastomer from between the nonextensible laminae. At the same time, the openwork structure of the mesh permits parallel movements between adjacent woof strands so as to accommodate twisting or torsional loading of the bearing.